Optimizing sales transactions, providing secure access to physical and digital assets, uniquely identifying individuals, and generally improving communications and data exchange are challenges faced by many businesses and organizations. Ensuring that these processes are safe, efficient, reliable, and simple is important to companies, merchants, service providers, users, and consumers. Well-known technologies such as user-specific magnetic cards (e.g., credit and debit cards, employee badges), and more recent developments such as contactless cards designed to allow access or authorization when placed near a compatible reader, are examples of attempts to address the need to instill efficiency and integrity in, for example, the general classes of transactions described above.